1. Field of the Invention
The present invention relates to computer system operations and, and, in particular, to the operation of a computer system executing instructions embedded in a read-only memory (ROM) device. More particularly, the present invention relates to the operation of an embedded computer system having a solid state read-only memory (ROM) containing both compressed and uncompressed operating instructions for the embedded system.
2. Background and Related Art
The present invention is directed to an improved method and apparatus for use with embedded computer systems. Embedded computer systems include a processor for performing instructions and input and output interfaces to collect data and transmit control signals. The instructions to be performed are typically stored on a read-only memory (ROM) device. Embedded computer systems are used, for example, to control automobile engine function and to provide a variety of other "intelligent devices."
Manufacturers using embedded computer systems are very conscious of the cost of each component of those systems. Small cost savings in embedded systems used in mass produced items such as automobiles are very important when considered over the production volume of the item. The size of ROM and size of random access memory (RAM) provided for an embedded system directly affect cost. ROM is less expensive than RAM and has the advantage of retaining data even when powered off (ROM provides non-volatile storage.).
ROM images are therefore used to contain the basic operating programs for an embedded device. A minimum amount of RAM is provided to store data readings and other changeable information. However, as increased function is added to an embedded system, the amount of data and instructions that must be stored in the ROM also increases. Manufactures are then faced with the prospect of having to add additional ROM or to decrease function. Additional ROM may be undesirable since it could significantly add cost due to a requirement to add an additional ROM device and the associated circuitry.
Thus, a technical problem exists of finding a way to put additional data and instructions in a ROM image without increasing the overall cost of an embedded device.